The present invention relates to a distributor type fuel-injection pump for distributing fuel to individual cylinders of an internal combustion engine, and more specifically to a distributor type fuel-injection pump provided with a rotor capable of pumping and distribution by only rotating.
A distributor type fuel-injection pump of this kind is disclosed in U.S. Pat. No. 2,935,062. This fuel-injection pump has a drive shaft (equivalent to the rotor) which is rotated by an engine. A cylindrical bore is formed in the drive shaft, extending at right angles to the axis of the drive shaft. A pair of pistons are slidably fitted in the cylindrical bore. Opposed end faces of the pistons define a fuel pumping chamber in the cylindrical bore. As the drive shaft rotates, the pistons are reciprocated by the action of cam means at a frequency equivalent to the number of the engine cylinders for each revolution of the drive shaft.
A cutout defining a control surface portion is formed on the outer peripheral surface of the drive shaft. The cutout is connected to the fuel pumping chamber by means of an inlet passage formed in the drive shaft. A control sleeve covering the cutout is axially slidably fitted on the outer surface of the drive shaft. Radial openings as many as the engine cylinders are formed in the control sleeve, arranged at regular intervals around the axis of the control sleeve. As the drive shaft rotates, the radial openings can communicate with the inlet passage by means of the cutout.
An outlet passage communicating with the fuel pumping chamber and a radial passage connecting with the outlet passage, the radial passage serving to distribute fuel to the individual engine cylinders, are formed in the drive shaft.
The operation of the aforementioned fuel-injection pump will now be described in brief. As the drive shaft rotates, the pistons are reciprocated, and the opening and closing of the inlet passage are controlled by the radial openings of the control sleeve and the control surface portion of the drive shaft. As the inlet passage is opened and closed and as the piston reciprocates, the fuel is fed through the inlet passage into the fuel pumping chamber, and is pressurized therein. The pressurized fuel is distributed to the individual engine cylinders through the outlet passage and the radial passage. The amount of fuel delivered from the fuel-injection pump depends on the closure time of the inlet passage, that is, the time of fuel pressurization in the fuel pumping chamber, after the fuel is fed through the inlet passage into the fuel delivery is decided by the unique shape of the control surface portion of the drive shaft and the axial position of the radial openings of the control sleeve.
This conventional fuel-injection pump is subject to the following drawback. Since the amount of fuel delivery depends on the shape of the control surface portion as a principal factor, the control surface portion need be worked with high accuracy for high-accuracy control of the amount of fuel delivery. However, it is technically difficult to accurately fabricate the control surface portion of the unique shape on part of the outer peripheral surface of the drive shaft. Also, the fabrication of the control surface portion requires higher cost.